The present invention relates to reel-type slot machines, and more particularly to a slot machine having stepper motor-driven symbol bearing reels, which offers improved protection against false displays such as may result from malfunctions of the stepper motor or tampering by a player.
In recent years reel-type slot machines have evolved from mechanical type machines wherein mechanical clutches were relied on to stop the reels at random locations, to electronic machines wherein a microprocessor randomly selects the game result, and the reels are driven to positions wherein symbols on the reels display the selected result. The present invention is directed to an improvement for such a machine.
In electronic reel type slot machines the reels are typically positioned by stepper motors, which may be contained in removable modules within the machine. The stepper motors respond to applied signals which are progressively phase-shifted relative to each other such that the stepper motor is caused to turn one element of rotation for each progression of the phase signals.
The phase signals are typically generated in a driver circuit, which responds to applied motor stepping pulses to advance the reel in increments. The motor stepping pulses are generated by a microprocessor, a predetermined number of pulses being generated to cause the motor to be incremented to a selected stopping position wherein the game result is displayed. In practice, the stopping position is determined by either counting the number of motor pulses occurring after a "home" marker on the reel has passed a fixed sensor, or by counting markers provided on the reel for each display position after the home marker has passed.
In either case, the potential exists for the reel to not be accurately positioned by the stepper pulses. This can occur if the motor fails to increment in response to an applied drive signal, or if the reel is mechanically retarded or advanced, as by tampering during or after application of the drive signals.
The present invention is directed to a reel-type slot machine having a display system wherein the movement of the reels is continuously monitored to detect such slipping or tampering, and wherein in such event, an alarm is sounded and further play is inhibited.
In particular, in the slot machine of the present invention monitoring is accomplished by sensing back-EMF on the stepper motor stator windings, and generating an alarm signal in the event such back-EMF exceeds a predetermined threshold level. The alarm signal is applied to the microprocessor game circuitry to inhibit the payout of a reward and prevent any further play of the slot machine.
Accordingly, it is a general object of the present invention to provide a new and improved reel-type slot machine.
It is a more specific object of the present invention to provide a reel type slot machine having a stepper motor driven display which provides improved protection against malfunctions and tampering.